Atherosclerosis is a complex process that involves the proliferation of vascular smooth muscle cells and the consequent narrowing of the vascular lumen. Stenosis of arteries also occurs after clinical angioplasty procedures, probably as a response to vascular injury. Platelet-derived growth factor (PDGF) is likely to be involved in stimulating smooth muscle cell proliferation in both of these clinical settings. Animal models of diet-induced atherosclerosis or balloon catheter injury of blood vessels can reproduce the vascular lesions seen in human disease. However it has been difficult to prove that PDGF is required for the proliferation of smooth muscle cells in vivo. The main goal of this proposal is to develop novel approaches to block PDGF action in vivo so that the role of this factor can be tested in animal models of atherogenesis. These approaches will be based on an understanding of the molecular biology of the PDGF receptor. Three types of protein-protein interactions have recently been shown to be required for signal transduction by PDGF receptors: ligand- receptor binding, receptor-receptor dimerization and receptor interactions three types of receptor antagonists will be generated: 1) Soluble antagonists consisting of portions of the extracellular ligand-binding region of the receptor will be used to prevent the interaction of PDGF with its cellular receptor; 2) Mutant PDGF receptors that form inactive heterodimers with wild type receptors will be expressed in isolated cells and in blood vessels in vivo and will thereby block the function of endogenous receptors; 3) Cytoplasmic portions of the receptor will be used to disrupt the interactions of receptors with key signalling molecules. The antagonists will be tested using a spectrum of methods from well- defined in vitro assays to transgenic animals. This proposal represents a focus on vascular disease and builds on work funded by this grant during the last seven years. The purification of PDGF receptors, cloning of receptor cDNA's, generation of antireceptor antibodies, studies of receptor dimerization, discoveries of signal transducing mechanisms and generation of receptor mutants have made it possible to design the experiments in this proposal. The results should provide new approaches for the study of the role of PDGF in vascular disease and should help devise new therapeutic strategies for blocking the actions of growth factors in vivo.